1Department of Pharmacology, School of Veterinary Medicine, University of Shiraz, Shiraz, Iran; 2Graduated from School of Veterinary Medicine, Islamic Azad University of Shahrekord, Shahrekord, Iran *Correspondence: H. Rajaian, Department of Pharmacology, School of Veterinary Medicine, University of Shiraz, Shiraz, Iran. E-mail: [email protected]
(Received 25 Jul 2005; revised version 8 Nov 2005; accepted 8 Jan 2006)
Tetracycline may be used to treat several types of bacterial diseases in ruminants. In addition,
tetracycline is added to food to promote the growth. There are few reports on the pharmacokinetics of tetracycline in sheep. Therefore, the objective of this study was to examine the pharmacokinetic characteristics of the drug in sheep. Ten apparently healthy mixed-breed sheep were administered 20 mg/kg tetracycline orally and intravenously with a time interval of two weeks. Blood samples were collected before and at various time intervals after the administration of the drug. Sera were separated, kept at -20°C, and analysed using fluorescence spectrophotometry. The volume of distribution (Vd), elimination rate constant
(Kel), half-life (t1/2), and clearance (ClB) of tetracycline after intravenous injection were determined to be 0.21
L/kg, 0.21/hr, 3.3 hr, and 0.73 ml/kg/min, respectively. When the drug was given orally, these parameters were found to be 0.37 L/kg, 0.12/hr, 5.8 hr, and 0.73 ml/kg/min, respectively. Moreover, the bioavailability of tetracycline after oral administration was around 55%. Key words: Tetracycline, Pharmacokinetics, Sheep Introduction
Ziv and Sulman, 1974; Bradley et al., 1982;
Xia et al., 1983a; Nouws et al., 1985; Riondet al., 1989; Meijer et al., 1993), sheep (Ziv
1986), goats (Jha et al., 1989; Escudero et al., 1994; Escudero et al., 1996), pigs (Xia et al., 1983b; Hall et al., 1989), dogs (Baggot
drug was first introduced for clinical use in
et al., 1977; Wilson et al., 1985) and horses
1952 and is still used both in small and food-
(Pilloud, 1973; Teske et al., 1973; Horspool
producing animals. Tetracyclines have been
and McKellar, 1990). Relatively little has
used in ruminants as both prophylactic and
ruminants. The objective of this study was to
characteristics of tetracycline in sheep after
susceptibility to the drug but also of the
a single oral or intravenous dose of the drug.
achieved in the animal’s body fluids. Drug
Materials and Methods
pharmacokinetics of tetracycline in different
animal species such as cattle (Pilloud, 1973;
had access to water and food ad libitum.
Iranian Journal of Veterinary Research, University of Shiraz, Vol. 8, No. 2, Ser. No. 19, 2007 Drug Pharmacokinetic analysis
1- Single intravenous dose: The blood
pooled from the available drug dosage form
concentration-time data were analysed by
non-linear least squares regression analysis
Iran). The volume of antibiotic solution—
(Fig. 1a). A non-compartmental analysis was
found to be appropriate to estimate the major
administered to each animal was calculated
pharmacokinetic parameters. Area under the
based on the body weight and a correction
concentration-time curve from time zero to
factor for the purity of the drug solution
trapezoidal rule with extrapolation to infinite
hydrochloride solution (Merck Co., Lot No.
time by dividing the last available blood
disposition rate constant; the apparent first-
Experimental design
order rate constant for elimination (Kel) was
In a cross-over design, five sheep were
phase of the log concentration-time data.
chloride intravenously through the right
The elimination half-life (t1/2) was calculated
jugular vein. Another five sheep were given
the drug at the same dose orally. After a
administration, the groups were switched.
Blood samples were collected from the left
jugular vein on -5, 5, 15, 30 and 60 min, and
intravenous injection of tetracycline. For the
a) Intravenous dose
oral route, blood samples were taken on -5,
1, 2.5, 3.5, 4.5, 7, 9, 13, 17 and 24 hrs after
administration of the antibiotic. Sera were
separated by centrifugation at 1500 g for 15
min and stored at -20°C until drug analysis
Tetracycline assay Time (hrs)
metry (Chang et al., 1992). In summary,
serum proteins were first precipitated by
b) Oral dose
addition of tricarboxylic acid solution. Then 0.3 M potassium hydroxide (2 ml) solution
serum samples or standards. After vortex,
tubes were kept in boiling water bath for 30
adjusted to 10 ml by addition of distilled
water. The fluorescence of each sample and
standards were determined by fluorescence
Scientific Instruments) at excitation and emission wavelengths of 333 and 450 nm,
respectively. The mean ± SEM recovery of
Time (hrs)
tetracycline was 87.4 ± 3.2 (n=5; CV<10%).
Fig. 1: Log blood concentration-time plot for
The sensitivity of the test was >2 µg/ml.
tetracycline (20 mg/kg) administered to sheep
Iranian Journal of Veterinary Research, University of Shiraz, Vol. 8, No. 2, Ser. No. 19, 2007
administration of tetracycline (Fig. 1b) was
best described by a one-compartment model
with first-order input (absorption). The
greater than its corresponding mean value
fraction of dose absorbed (F) was estimated
(P≤0.05). The apparent Vd of tetracycline in
intravenous administration of the drug. Kel
sheep was found to be 0.37 L/kg; and ClB
was obtained from the slope of the log-linear
portion of the elimination phase of serum
Table 1: Disposition kinetics in sheep given a
were calculated as described earlier and
single oral or intravenous dose of tetracycline hydrochloride (20 mg/kg) Statistical analysis
Means were compared by Student’s t-test for
independent samples. The F-test was used to
determine which compartmental model best
described the kinetics of tetracycline in
AUC (area under the serum concentration versus
Intravenous dose
After intravenous injection of 20 mg/kg
distribution); Kel (elimination rate constant); t1/2
tetracycline hydrochloride, an initial concen-
(elimination half-life); ClB (clearance)
tration of 200 µg/ml was attained in serum.
Six hrs later, the concentration decreased to
Discussion
one-tenth of its initial level, i.e., to almost 20
µg/ml. The mean log blood concentration-
The serum concentrations of tetracycline
time plot (Fig. 1a) for tetracycline was non-
in sheep were proportionally similar to those
linear after intravenous administration of the
obtained for doxycycline and minocycline in
drug; the disappearance of the drug from
with a rapid distribution phase (t1/2 <0.5 hr)
tetracycline, administered intravenously to
followed by a slow elimination phase (t1/2 ≈
distribution of tetracycline was 0.21 L/kg.
described for cows and chickens (Ziv and
The blood clearance of tetracycline in sheep
was found to be 0.73 ml/min/kg (Table 1).
Oral dose
Varmaand Paul, 1983). However, marked
(251 µg hr/ml) with that of intravenous dose
pharmacokinetic parameters for tetracycline
availability (F) of the drug was almost 55%.
After oral administration of tetracycline,
Two hrs following oral administration of the
the drug concentration decreased to less than
3 µg/ml after 24 hrs. Bearing in mind that
the antimicrobial activity of tetracycline in
attained. The maximum blood concentration
(Cmax) was almost 22 µg/ml that was attained
concentrations >0.5 µg/ml (Pijpers et al.,
almost four hrs after drug administration
(Tmax = 4 hrs). The decline in tetracycline
possibly be attainable with administration of
Iranian Journal of Veterinary Research, University of Shiraz, Vol. 8, No. 2, Ser. No. 19, 2007
problem of change in the rumen flora should
Table 2 illustrates the pharmacokinetic
intravenous injection, may indicate that
diffusion of tetracycline out of blood vessels
tetracycline after intravenous injection of the
is poor. The apparent Vd after oral adminis-
drug in sheep is almost five times less than
tration of tetracycline was more than that
the value found in rabbits (Percy and Black,
after intravenous route (0.37 vs 0.21 L/kg,
1988). It is, however, similar to the value
reported for chickens (Anadon et al., 1985).
intestinal tissues and antibiotic adsorption to
doxycycline in goats (Jha et al., 1989; Table
the food contents, particularly of the rumen.
The drug elimination t1/2 for tetracycline
tetracycline t1/2 and Kel indicates that the
in sheep is close to those values reported for
drug is eliminated at a slower rate when
Paul, 1983), chlortetracycline in cows and
(Table 1). This difference in part can be due
ewes (Ziv and Sulman, 1974), tetracycline in
to the durable nature of the drug absorption
pigs (Kniffen et al., 1989) and minocycline
Furthermore, the longest t1/2 (around17 hrs)
poorly studied in animal species, particularly
is reported for doxycycline in goats (Jha et al., 1989); the shortest t1/2 (2 hrs) belongs to
examined the disposition of tetracycline in
tetracycline in rabbits (Percy and Black,
some species, though, numerous reports are
available on other members of tetracyclines.
similar to that in horses for oxytetracycline
(Horspool and McKellar, 1990). The largest
intravenous administration of the drug to
clearance is reported for oxytetracycline in
sheep will remain more than 3 µg/ml for at
least 12 hrs. The t1/2 of tetracycline was also
reported to be 11.2 hrs—almost three times
between the pharmacokinetic properties of
Table 2: Pharmacokinetics of tetracyclines following intravenous administration in different animals
*Vd (apparent volume of distribution); †Kel (elimination rate constant); ‡t1/2 (elimination half-life); §ClB
Iranian Journal of Veterinary Research, University of Shiraz, Vol. 8, No. 2, Ser. No. 19, 2007
tetracyclines in sheep and other domestic
administration. Equine Vet. J., 22: 284-285.
animals indicate the importance of pharma-
cokinetic studies for establishing a correct
Singh, SD (1989). Pharmacokinetics data on
doxycycline and its distribution in different
biological fluids in female goats. Vet. Res. Commun., 13: 11-16.
Acknowledgements
Kniffen, TS; Bane, DP; Hall, WF; Koritz, GD
pharmacokinetics, and plasma concentration
Mr. Jalaee for his technical assistance.
of tetracycline hydrochloride fed to swine.
Financial support by Shiraz University and
Islamic Azad University of Shahrekord is
Laczay, P; Semjen, G; Lehel, J and Nagy, G
(2001). Pharmacokinetics and bioavailability
of doxycycline in fasted and non-fasted broiler chickens. Acta Vet. Hung., 49: 31-37.
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